Graphene base transistor and method for making the same

Abstract

A graphene base transistor comprises on a semiconductor substrate surface an emitter pillar and an emitter-contact pillar, which extend from a pillar foundation in a vertical direction. A dielectric filling layer laterally embeds the emitter pillar and the emitter-contact pillar above the pillar foundation. The dielectric filling layer has an upper surface that is flush with a top surface of the emitter pillar and with the at least one base-contact arm of a base-contact structure. A graphene base forms a contiguous layer between a top surface of the emitter pillar and a top surface of the base-contact arm. A collector stack and the base have the same lateral extension parallel to the substrate surface and perpendicular to those edges of the top surface of the emitter pillar and the base-contact arm that face each other.

The invention claimed is: 
     
       1. A graphene base transistor, comprising, on a semiconductor substrate surface:
 at least one emitter pillar and at least one emitter-contact pillar, which extend from a pillar foundation, through which they are electrically connected, in a vertical direction pointing perpendicularly away from the substrate surface; 
 a dielectric filling layer laterally embedding the emitter pillar and the emitter-contact pillar, and separating them from each other in regions above the pillar foundation, 
 an electrically conductive base-contact structure, which is either arranged on or embedded in the dielectric filling layer and which includes
 a) a base-contact face, which is arranged at a lateral distance from the emitter pillar, and, 
 b) at least one base contact arm, which extends from the base-contact face in a direction parallel to the substrate surface and passes between the top surfaces of the emitter pillar and of the emitter contact-pillar without directly contacting them; 
 
 wherein the dielectric filling layer has an upper surface that is flush with a top surface of the emitter pillar and with the at least one base-contact arm 
 a base layer of graphene forming a contiguous layer that extends between and covers an immediately adjacent top surface of the emitter pillar and at least a part of an immediately adjacent top surface of the at least one base-contact arm; 
 a collector stack that comprises at least a collector-barrier layer, which is arranged immediately on the graphene layer, and an electrically conductive collector layer, which is arranged on the collector-barrier layer, 
 wherein the collector stack and the base layer have the same lateral extension in a direction that is parallel to the substrate surface and perpendicular to those edges of the top surface of the emitter pillar and the base-contact arm that face each other. 
 
     
     
       2. The graphene base transistor of  claim 1 , wherein the top surface of the emitter pillar is formed by an emitter-barrier layer that is made of a dielectric material while the rest of the emitter pillar is made of a semiconductor. 
     
     
       3. The graphene base transistor of  claim 1 , wherein the emitter pillar has the shape of a rectangular parallelepiped or of a truncated cone. 
     
     
       4. The graphene base transistor of  claim 1 , comprising two emitter-contact pillars arranged on opposite lateral sides of the emitter pillar. 
     
     
       5. The graphene base transistor of  claim 4 , wherein the base-contact structure has two base-contact arms that extend in parallel to each other from the base-contact face on opposite sides of the emitter pillar and that pass between respective edges of the top face of the emitter pillar and of the emitter contact pillar. 
     
     
       6. The graphene base transistor of  claim 5 , wherein the collector stack covers a lateral region extending between and including at least a part of the base-contact arms. 
     
     
       7. The graphene base transistor of  claim 1 , wherein the base-contact structure is made of either Ti, TiN, Ta, Ni, Al or Cu or a combination of at least two of these materials. 
     
     
       8. The graphene base transistor of  claim 1 , wherein the graphene base layer covers only a part of a lateral extension of the at least one base-contact arm, wherein the lateral extension is measured in a direction perpendicular to the longitudinal direction of the base-contact arm. 
     
     
       9. The graphene base transistor of  claim 1 , wherein the at least one base contact arm includes at least one opening that is laterally positioned on the at least one base-contact arm and that extends through the base-contact arm in a vertical direction, which points perpendicular to the substrate surface, and wherein the graphene base layer covers the at least one opening. 
     
     
       10. An electronic component, comprising at least one graphene base transistor according to  claim 1  and at least one MOS-transistor, a passive electronic device, an optoelectronic device, a photonic device, or a MEMS device on the same silicon or silicon-on-insulator substrate. 
     
     
       11. A method for fabricating a graphene base transistor, comprising
 providing a silicon substrate surface; 
 fabricating an electrically conductive pillar foundation on the substrate surface, at least one emitter pillar and at least one emitter-contact pillar, which extend from the pillar foundation in a vertical direction pointing away from the substrate surface; 
 embedding emitter pillar and the emitter contact pillar in a dielectric filling layer in regions above the pillar foundation, and fabricating an upper surface of the filling layer as flush with a top surface of the emitter pillar; 
 fabricating on the dielectric filling layer an electrically conductive base-contact structure, which includes
 a) a base-contact face, which is arranged at a lateral distance from the emitter pillar, and, 
 b) at least one base-contact arm, which extends from the base-contact face in a direction parallel to the substrate surface and passes between the top surfaces of the emitter pillar and of the emitter contact-pillar without directly contacting them; 
 
 covering a contiguous lateral region extending at least between and including the top surface of the emitter pillar and the at least one base-contact structure with a graphene layer; 
 fabricating a collector stack that comprises at least a collector-barrier layer, which is arranged immediately on the graphene layer, and an electrically conductive collector layer, which is arranged on the collector-barrier layer, 
 wherein the collector stack and the base layer are subsequently structured together to give them the same lateral extension in a direction that is parallel to the substrate surface and perpendicular to those edges of the top surface of the emitter pillar and the base-contact arm that face each other. 
 
     
     
       12. The method of  claim 11 , wherein fabricating the electrically conductive pillar foundation, the at least one emitter pillar and at least one emitter-contact pillar comprises
 structuring the emitter layer by masked anisotropic etching to form the emitter pillar and the emitter-contact pillar, and stopping the etching before reaching the foundation mesa in order to obtain the pillar foundation. 
 
     
     
       13. The method of  claim 12 , wherein fabricating the emitter contact pillar comprises, before fabricating the collector stack, fabricating a metallically conductive emitter-contact face on the exposed top surface of emitter layer at the position of the emitter-contact pillar. 
     
     
       14. The method of  claim 13 ,
 wherein fabricating the base-contact structure comprises fabricating at least one opening in the at least one base-contact arm that is laterally positioned on the at least one base-contact arm and that extends through the base-contact arm in a vertical direction, which points perpendicular to the substrate surface. 
 
     
     
       15. A method for fabricating an electronic component, comprising
 a) covering a first lateral region of a silicon substrate or silicon-on-insulator substrate of with a first masking layer; 
 b) fabricating a graphene transistor according to a method of  claim 11  in a second lateral region on the silicon surface of the substrate; 
 c) removing the first masking layer from the first lateral region; 
 d) covering the second lateral region with a second masking layer 
 e) fabricating at least one other active or passive device in the first lateral region on the silicon surface of the substrate; 
 f) removing any remaining masking layer 
 
       wherein the sequence of steps d) to f) is performed either before or after the sequence of steps a) to c). 
     
     
       16. The method of  claim 11 , wherein fabricating the emitter contact pillar comprises, before fabricating the collector stack, fabricating a metallically conductive emitter-contact face on the exposed top surface of emitter layer at the position of the emitter-contact pillar. 
     
     
       17. The method of  claim 11 , wherein fabricating the base-contact structure comprises fabricating at least one opening in the at least one base-contact arm that is laterally positioned on the at least one base-contact arm and that extends through the base-contact arm in a vertical direction, which points perpendicular to the substrate surface.